Communication equipment typically operates around a set of rules. These rules govern the interactions of discrete elements of the communications network. In the case of data communications, the rules, called protocols, are programmed rather than built into the hardware. The protocols are typically a set of rules for grouping bits and characters (framing), error detection and correction (error control), the numbering of messages (sequencing), separating control characters, sorting, receiving and sending (line control), and actions required on initiations (start-up control) and actions required on termination (time-out control). The protocols are typically constructed on a frame, with bits grouped into define sequences and with the positions of the groups defining the meaning of the message. Examples of these protocols are well known in the art and are not discussed here.
Also well known in the art are the kind of communications equipment that use these protocols. Because this communication is well known, the type of equipment is not discussed.
For reference purposes, communications using message packets constructed on a frame such as to be used to practice this invention are described in ANSI/IEEE Standard 802.3, Information Processing Systems Local Area Networks; ISBN 1-55937-805-4. Further, systems using message packets, the manner of construction and use are well known, and for that reason are not discussed here. Examples of such systems are shown in U.S. Pat. No. 4,745,593, Arrangement For Testing Packet Switching Networks; U.S. Pat. No. 4,558,428, Data Transmission System Adapted to Facilitate Detection of Safe Receipt of the Transmitted Data Frame By a Receiving Station; U.S. Pat. No. 5,056,085, Fourth and Forward Routing for Broadcast Packets In Packet Switching Networks; U.S. Pat. No. 5,086,428, Reliable Broadcast and Information In a Wide Area Network.
Within any data communications system, one station may be dedicated to control of the network. That is, a master node may be programmed to initiate messages and to terminate messages that circulate through the system.
The use of a master node can be sufficient where an undelivered message or a message to be delivered circulates through the master node or in only one direction and complete control over the system is thereby insured at the master node. For example, the master node may be a switch. In functioning as a switch, the master node may break the path and in that way prevent recirculation of a message
However, in some networks, such as networks having internal circulating loops, and permitting message propagation two or more directions, it is possible for the message to be misdirected such as by continuous circulating within an internal loop, without providing any indication of such malfunction to the master.